The invention relates to a catalytic system which is advantageous in hydroconversion of hydrocarbon feeds such as naphtha.
Many nations have implemented environmental legislation and energy conservation policies which idealize stringent rules in order to drastically reduce emissions of contaminants such as sulfur.
Clean air act amendments and other legislation have mandated reductions in emission levels in terms of sulfur, olefins, aromatics and the like, which are considered to contribute to contamination levels.
One source of volume to the gasoline pool is naphtha, particularly FCC naphtha, which is the source of approximately 80% of the sulfur in the gasoline pool. Further, such FCC naphtha also constitutes approximately 40% (vol) of the total amount in the gasoline pool.
Clearly, FCC naphtha is an important feed to be treated for reduction of sulfur.
Various hydroconversion processes have been developed for treating such feedstocks in order to reduce sulfur content thereof. One such process involves a first stage wherein sulfur and nitrogen are substantially removed, but also wherein olefins contained in the feedstock are greatly saturated. In such processes, the saturation of olefins results in a loss in octane values, and a second stage treatment is employed in order to recuperate the lost octane values.
In the reformulation of gasoline, an octane loss is expected to occur due specifically to hydrogenation of olefins (HDO). This loss is compensated or recovered through cracking reactions, isomerization, aromatization, and the like, which can be accomplished during the aforesaid second stage of the reaction.
Hydroconversion catalysts are conventionally sensitive to nitrogen in the feed, and can require pre-treatment of the feed to remove nitrogen, which also adds a step and additional cost to the preparation process.
Of course, any required second stage or step adds to the processing cost for fractions such as naphtha, and therefore the need exists for improved methods of reduction in sulfur and nitrogen content without adverse impact on octane values (RON, MON).
It is therefore the primary object of the present invention to provide a catalyst and process for using same whereby the need for additional reaction zones is avoided.
It is a further object of the present invention to provide a catalyst and process for using same wherein hydrodesulfurization and hydrodenitrification are accomplished.
It is a still further object of the invention to provide a catalyst which is resistant to nitrogen and can avoid the need for pre-treatment to remove nitrogen from the feed.
Other objects and advantages of the present invention will appear herein below.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
According to the invention, a hydroconversion catalyst is provided which is effective in hydrodesulfurizing feedstocks while preserving octane numbers, which catalyst comprises a support comprising a mixture of zeolite and alumina, said zeolite having an Si/Al ratio of between about 1 and about 20, and an active phase on said support and comprising a first metal selected from group 6 of the periodic table of elements, a second metal selected from the group consisting of group 8, group 9 and group 10 of the periodic table of elements, and a third element selected from the group 15 of the periodic table of elements.
In further accordance with the present invention, a process for hydroconversion of hydrocarbon feedstock is provided, which process comprises providing a hydrocarbon feed having an initial sulfur content and an initial olefin fraction; providing a hydroconversion catalyst comprising a support comprising a mixture of zeolite and alumina, said zeolite having an Si/Al ratio of between about 1 and about 20, and an active phase on said support and comprising a first metal selected from group 6 of the periodic table of elements, a second metal selected from the group consisting of group 8, group 9 and group 10 of the periodic table of elements, and a third element selected from the group 15 of the periodic table of elements, and exposing said feed to said catalyst under hydroconversion conditions so as to provide a product having a final sulfur content less than said initial sulfur content. The olefin content of the final product varies depending upon the operating conditions used to process the feedstocks. In some cases, the olefin retention is very high and for other cases, the olefin content is substantially lower than the initial olefin content. Advantageously, however, the catalyst of the present invention provides for increased ratio of iso-paraffins to n-paraffins and reduction in molecular weight of the n-paraffins which serve to improve octane ratings of the product and help make up for the olefin loss which itself is reduced in any event.